Sample insertion vacuum lock and probe assembly for mass spectrometers

ABSTRACT

A sample insertion vacuum lock and probe assembly for use in mass spectrometers is disclosed in which an axially extending sample carrier is mounted for reciprocal movement into and out of an ion chamber. Electrical connection with the sample carrier probe is made through sliding engagement of the probe with an electrical contact support assembly mounted in the ion chamber. A vacuum lock and a vacuum system is provided to insure that the vacuum in the ion chamber is not disturbed. Mechanical locking means and positioning means are included to prevent accidental destruction of the vacuum and to precisely position the sample within the ion chamber.

United States Patent [72] Inventors Richard E. Perrin;

Billy A. Hopper, both of Tulsa, Okla. [21] Appl. No. 837.549 [22] FiledJune 30. 1969 [45] Patented June 29, 1971 [73] Assignee Avco Corp.

Tulsa. Okla.

[54] SAMPLE INSERTlON VACUUM'LOCK AND PROBE ASSEMBLY FOR MASSSPECTROMETERS 2 Claims, 3 Drawing Figs.

[52] U.S.Cl 250/419 S. 250/4l.9 SE [5 I] Int. Cl H0lj 39/34 {50] Fieldof Search 250/419 SE, 41.9 S

[56] References Cited UNITED STATES PATENTS 2,756,341 7/1956 White250/419 Primary Examiner-William F. Lindquist Attorneys-Charles M. Hoganand Eugene C. Goodale ABSTRACT: A sample insertion vacuum lock and probeassembly for use in mass spectrometers is disclosed in which an axiallyextending sample carrier is mounted for reciprocal movement into and outof an ion chamber. Electrical connection with the sample carrier probeis made through sliding engagement of the probe with an electricalcontact support assembly mounted in the ion chamber. A vacuum lock and avacuum system is provided to insure that the vacuum in the ion chamberis not disturbed. Mechanical locking means and positioning means areincluded to prevent accidental destruction of the vacuum and toprecisely position the sample within the ion chamber.

72 PUMP PUMP PATENTEUJUNZSISH 3.590243 SHEET 2 OF 3 INVENTORS. RICHARDE. PERRIN BY BILLY A. H

SAMPLE INSERTION VACUUM LOCK AND PROBE ASSEMBLY FOR MASS SPECTROMETERSBACKGROUND OF THE INVENTION The present invention relates to vacuumlocks and more particularly to vacuum locks and specimen carrying probesused in mass spectrometers for changing specimens to be analyzed.

The analysis of samples by standard surface ionization mass spectrometrytechniques requires that the sample undergoing analysis be inserteddirectly into the mass spectrometer ion source. The ion source of themass spectrometer standardly operates at a pressure no greater than 1 l0torr. It is therefore necessary, in operation, to provide either a rapidmethod of pumping out the ion source after changing a sample or a methodof inserting the-sample without breaking the mass spectrometer vacuum.

Previous techniques; typically utilized in mass spectrometric analyses,provided a method of removing atmospheric pressures from the ion sourceregion after insertion of the sample. Adsorbtion of atmospheric waterincreases the time required to achieve operational vacuum; typically aminimum of l5minutes is required to reach operational levels. Adsorbtionalso reduces source life due to reactions between it and the samplematerials resulting in rapid contamination of the ion source.

One common method of inserting samples into a thermal emission massspectrometer consists of venting the ion source to atmosphere andinserting the filament hat carrying the sample through the back coverflange. This method requires that the entire ion sourcebe pumped outafter each new saniple. In addition to severely limiting samplethroughput, this procedure also increases contamination to the ionsou'fce and decreases filament life on the ion gauges.

Two approaches have been used by others to eliminate these problems. Thefirst approach consists of mounting several filament hats on a rotatablewheel. This approach has two undesirable features. The chance of crosscontamination between filaments is greater and the life of theelectrical con tacts is extremely short. 7

The second approach has been to use a vacuum lock. A vacuum lock is adevice which permits the interchange of some piece of equipment into orout of a vacuum chamber without loss of the vacuum. In the field of massspectroscopy, the use of a vacuum lock assembly to interchangesamplesfor ionization by the thermal emission method has proven to behelpful, particularly to those investigators whose needs require a highquantity of routine analyses to be performed. In such locks, thespecimen carrier is moved by a thrust rod through a valve aperture fromthe locked chamber into the analyzer, or other vacuum chamber, andsubsequently removed. The shaft of the sample probe is usually insertedthrough a series of differentially pumped chambers divided by Teflon orViton seals. In this manner the pressure in the final chamber can beequalized with the pressure in the ion source chamber before the valvebetween the chambers is opened. These systems have been quite expensiveto build. The principal cause for this expense is the practice of makingelectrical connections to the filaments through vacuum seals in the backof the sample probe. The high accelerating voltages needed forionization require large feedthroughs which increase the sample probediameter to at least three inches. Such large probes cannot beconveniently handled without elaborate and expensive mechanical orelectrical drive mechanisms.

In accordance with the present invention, the drawbacks of presentlyexisting sample insertion vacuum lock devices are overcome by providinga vacuum lock having greater utility and efficiency. The improvedassembly of the present invention provides for the precise alignment offilaments and eliminates the need for the usual metal filament hat. Allelectrical connections are made as the-sample carrier slides intoposition, thus eliminating the need for insulated vacuum feedthroughs inthe probe assembly. The diameter and size of the sample carrier andprobe are significantly smaller than previous devices so that no specialvalves or drive mechanisms are required and the cost of the vacuum lockis significantly reduced.

SUMMARY OF THE INVENTION The present invention provides an improvedsample insertion vacuum lock and probe assembly for use in massspectrometers which eliminates or minimizes the disadvantagesencountered in previous systems utilizing sample insertion techniques.The invention comprises a novel sample insertion probe assembly whichpermits axial insertion of thesample carrier and probe into the ionsource. Axial insertion allows a more precise location of the filamentsin relation to the source plates and eliminates the need for attachingthe back source plates to the insertion probe; thus permitting the usageof sliding contacts which make direct electrical contact with thespecimen carrier as the specimen is inserted.

The electrical contacts are located within the vacuum system or ionchamber and the usage of sliding and biased electrical contacts insuresconstant continuous electrical connection between the electrical systemand filaments. Locating electrical contacts in this manner eliminatesthe usage of high voltage vacuum feedthroughs in the probe assembly. Thesample carrier and driver probe are of a smaller diameter and thusreduces the volume of air to-be evacuated from a differential pumpingchamber and also contributes to the usage efficiency of the massspectrometer. A mechanical probe positioner or position limiting deviceprovides a fail safe mechanical system to prevent destruction of thevacuum within the ion source region and also to prevent jamming of thesample into the gate valve on insertion.

Other details, uses, and advantages of this invention will becomeapparent as the following description of the exemplary embodimentthereof presented in the accompanying drawings proceeds.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings show apresent exemplary embodiment of this invention in which:

FIG. 1 is a side view partially in cross section illustrating anexemplary embodiment of this invention showing the specimen carrier andprobe in operational position within the ion chamber;

FIG. 2 is an end view' taken on the line 2-2 of FIG. 1, illustrating theelectrical support assembly; and

FIG. 3 is a cross-sectional view of the electrical contact assemblytaken on the line 3-3 of FIG. 2.

DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT Reference is now made to FIG.1 which shows one exemplary embodiment of the improved sample insertionvacuum lock and probe assembly which is designated generally by thereference numeral 10 and is mounted to a vacuum chamber such as a massspectrometer ion chamber 12. Conventionally mounted within the ionchamber 12 is an ion source, shown generally as 14, adjacent to whichthe specimen to be analyzed must be placed.

The specimen to be analyzed is placed on filament elements 16 and 18(FIG. 2). Filaments l6 and 18, together with an ionization filament 17,are secured to a specimen or sample carrier 20. The carrier 20 isattached in axial alignment with a driver probe 22 in any convenientmanner, such as by threadable engagement with a threaded end portion ofprobe 22. On the other end of probe 22 is a handle element 25 for easein the insertion and removal of the probe assembly.

The electrical energy necessary to cause the vaporization and ionizationof the specimen is supplied to the filaments through a novel electricalcontactor ring and switch assembly 23 which is best seen in FIGS. 2 and3.

The contact support assembly 23 includes a supporting ring or plate 24which is mounted in the ion chamber by any suitable means. The plate 24has an aperture 26 formed therethrough. A plurality of contact members,2811-231, are mounted to the plate 24 with one end of each contactmember extending into the aperture area. It is also seen that the axisof each contact member 28 is normal to the axis of the plate aperture.

Each respective contact member 28 includes an outer casing 30 having acentral stepped passageway 32 formed therethrough. An inner contactelement 34 is slidably mounted in the passage 32 and biased outwardly orinto the aperture area 26 by any resilient means such as spring 36. Itis seen that the spring 36 abuts against the stepped inner surface ofpassageway 32 at the one end and against the sliding member 34 at theother.

Apertures 33 and 40 are respectively formed though outer casing 30 andthe sliding member 34. It is also noted that the aperture 38 is ofgreater diameter than the aperture 40. An electrical lead or connectorwire 42 extends through aperture 40 and is secured to contact 34 by anysuitable means such as a setscrew 43. Thus, with the lead 42 connectedto member 34, the sliding movement of member 34 is limited to the amountof clearance between the lead 42 and the aperture 38 of casing 30. Lead42 is connected to a source of energy which provides the electricalenergy for the vaporization of the specimen.

The sample carrier 20 is mounted for reciprocal movement through theaperture 26 in a manner which will be described herebelow. The carrier20 is made of an insulating material such as a low water adsorbtionceramic and is mounted to be coaxial with the axis of the plate aperture26. Stationary contact members 44 are secured to the outer surface ofthe sample carrier 20 by any suitable means such as screws 46. A likenumber of contact members, 44a-44f, as there are contact members 28 ofthe contact support assembly 23, are mounted on the sample carrier sothat each stationary contact member cooperatively engages a slidablecontact element. Sample carrier 20 has a groove or channel 48 formedthereon in which the contact members 44 are mounted. This facilitatesfor ease in construction of the contact elements 44 in that the slopingedge need not come to a point to insure ease in sliding engagement withthe member 34.

Filaments 16, 17 and 18 each consist of two leg portions and aninterconnecting element between the respective leg portions. Eachfilament leg is respectively secured to a conducting member or rodSOa-Stlf. Each of the conducting rods is connected to a correspondingstationary contact member by the screws 46. Hence, there is electricalcontinuity between each electrical lead 42 and each filament leg throughthe respective contacts 34 and 44, screws 46, and conducting rod 50. Asan example, the filament l6 legs are attached to rods 50c and 50f whichare in turn in electrical contact with stationary contacts 44c and 44f.

Referring again to FIG. 11, the assembly may be considered, whenassembled, as a one-piece unit which is attached to the ion chamber 12through an adapter plate which is secured to the ion chamber by anyconventional means such as bolts. Thus, the entire assembly 10 may beremoved as one piece when desired. However once the assembly 101 ismounted to the ion chamber 12, specimens may be inserted and removedfrom the chamber without destroying the vacuum therein as will beexplained herebelow.

A standard commercially available, high-vacuum gate valve showngenerally as 52 isolates the vacuum within chamber 12 from theatmosphere whenever the probe 22 is withdrawn. The gate valve 52 isattached by suitable means to the adapter plate. Extending axiallyoutward from the valve 52 is an outer casing 54 which, when the probe 22is inserted therethrough, defines chambers 56 and 58. An O-ring 60 ismounted within casing 54 to coact with the probe 22 and form a sealseparating chambers 56 and 58. An O-ring 62 is mounted at the outwardend of the casing 54 to coact with the probe 22 and form a seal betweenchamber 56 and atmosphere. A jam nut 64 threadably engages the end ofcasing 54 and is tightened thereon so as to compress the O-ring 62 toform a tight seal.

A conduit 66 is in communication between chamber 56 and fore pump 68. Avalve 69 is placed in conduit 66 between the chamber 56 and fore pump63. A conduit 70 is in communication between the chamber 58 anddiffusion pump 72. A valve 71 is inserted in the conduit 70 betweenchamber 58 and pump 72. A conduit 74 and valve 76 are placed upstream ofvalves 69 and 71.

The pumps and valving assemblies provide for two stages of differentiaLpumping across the surface of the probe 22 when the probe is insertedtherethrough. In operation, the valves are initially in a closedposition with the probe 22 and sample carrier 20 withdraw from theassembly. It is also noted that the gate valve 52 is closed whenever theprobe 22 is withdrawn. To provide the differential pumping, the probe 22with sample carrier 20 attached is inserted into the casing 54 to engage0- rings 60 and 62. At this time, valves 69 and 76 are opened and forepump 68 will reduce the pressure in chambers 56 and 58 to a pressure ofabout 50 microns in the first stage operation. Valve 76 is closed andvalve 71 is opened to bring chamber 58 in communication with thediffusion pump 72 for second stage operation. Pumping during this stageis continued until the pressure in the chamber 58 is reduced to theinstrument vacuum pressure approximately l l0 torr. When this pressureis reached, the high-vacuum gate valve 52 can be opened without fear ofdestroying the instrument vacuum within ion chamber 12 and the samplecarrier 20 and probe 22 can be inserted into specimen vaporizationposition. The operational instrument vacuum in the second stageoperation is rapidly achieved due to the extremely small Volume ofchamber 58 to be evacuated.

A probe-positioning device and safety device is shown generally as 78.The positioning device 78 includes a shaft 30 which is pivotally mountedat 82 to a suitable clamp 84 which is secured about casing 54. Bolt 85serves as a height-adjusting element so that shaft 80 may be positionedparallel with casing 54. A guide member 86 is adjustably secured to theshaft 80 by suitable means such as setscrews 88. An axial groove 90 isformed in guide 86 for receiving a dowel or pin 92 which is mounted inhandle 25. Guide 86 is positioned along shaft 80 to prevent theovertravel of probe 22 and carrier 20 which, if overtravel occurred,would result in damage to the ion source 14 and the specimen carryingfilaments. Groove 90 also serves as a positioning guide to properlyalign the filaments with the ion source. In other wordsf the probe 22 isinserted until the pin 92 engages the inner end of groove 90 and thusprecisely positions and aligns the filaments relative to the ion source14.

A stop member 94 is attached near the outer end of shaft 80 and servesto prevent the inadvertent destruction of the ion chamber vacuum duringwithdrawal of the probe 22 and also to prevent destruction of the gatevaLve 52 and filament elements upon insertion of the probe 22. With theshaft 80 in the parallel to casing 54 position, the shaft 22 can only beaxially retracted until the pin 92 engages side 96 of stop member 94.This position is shown in the phantom line of FIG. 1. At this position,the sample carrier 20 is also shown in phantom lines. Hence, when thisposition is reached the gate valve 52 may be closed to isolate the ionchamber 12 vacuum from atmosphere. To complete the withdrawal of probe22, such as to obtain a new specimen, valves 69, 71 and 76 are closed,shaft 80 is raised about its pivot point 82 to clear pin 92 (as shown inphantom lines) and shaft 22 is withdrawn the remainder of the way out ofcasing 54.

Prior to insertion of the probe 22, the shaft 80 is once again returnedto the parallel position. Probe 22 is inserted in casing 54 until pin 92engages side 98 of the stop member 94. At this point, the differentialpumping may be started as previously described.

In operation, a sample specimen is evaporated to dryness on the legconnecting portion of filaments 16 and 18. The filaments are theninserted into the respective conducting rods 50 on the end of theceramic sample carrier 20. The carrier 20, with the filaments attachedthereto, is attached to the driver probe 22 and the loaded probe isinserted into the casing 54 until pin 92 engages side 98 of the stopmember 94. Valves 69 and 76 are opened to allow the first stagedifferential pumping to bring the chamber 56 and 58 down to theapproximate 50- micron level. At this time, valve 76 is closed and valve7] opened to allow the diffusion pump 72 to evacuate chamber 58 down tothe instrument vacuum pressure. When chamber 58 has reached the ionchamber vacuum pressure, gate valve 52 is opened, shaft 80 is rotatedabout its pivot point and probe 22 inserted until pin 92 clears stopmember 94. The shaft 80 is returned to its parallel position and probe22 is inserted to maximum depth through the assembly 10 until pin 92reaches the inner end of groove 90. At this point, the filament elementshave been properly positioned relative to the ion source and theelectrical contacts on the sample carrier have made contact with thespring-loaded contacts of the switch assembly 23. The filament powersupplies are then activated and vaporization and ionization of thespecimen takes place. After sample analysis, the filament power suppliesare turned off and the ceramic sample carrier 20 is allowed to coolprior to withdrawal from the ion source. After cooling of the carrier20, the probe 22 is withdrawn from the ion chamber until pin 92 engagesside 96 of stop member 94. At this position, gate valve 52 is closed toisolate the ion chamber 12 from atmosphere. Valves 69 and 71 are closed,shaft 80 rotated about its pivot point and probe 22 is completelywithdrawn for the attachment ofa new sample specimen.

The invention in operation, has proven a capability of loading a sampleof uranium into the instrument and returning the source pressure to therequired operation vacuum range of 1 l0 torr in less than 3 minutes.Insertion of the same sample utilizing standard techniques; venting thesource region and then pumping down after the sample insertion typicallyrequires a minimum of 25 minutes to return the pressure to operationallevels of 1x10 torr. Thus, this invention, at a minimum, doubles sampleoutput and efficiency of the instrument to which it is attached. Anadditional benefit is the doubling of the source life of the massspectrometer due to elimination of contaminant from the ion source. itis seen that by making use of the novel location of the electricalcontacts within the vacuum system, the usage of sliding and springloadedelectrical contacts insures constant continuous electrical flow.Locating electrical contacts in this manner eliminates the use ofhigh-voltage vacuum feedthroughs in the probe. This feature enables theprobe design to be ofa smaller diameter, thus reducing the volume of airto be evacuated from the differential chamber and contributing to theusage efficiency of the mass spectrometer.

The use of an axial movement of the probe is advantageous since previousdevices utilized probes inserted at right angles to the direction of ionbeam travel. This invention inserts the probe in axial alignment intothe ion source, thus permitting first, a more precise location of thefilaments in relation to the source plates and ion beam, and second, iteliminates the need for attaching the back source plates to theinsertion probe permitting the usage of sliding contacts which makedirect electrical contact as the sample is inserted.

A further advance to the art of this invention is the use of the probepositioner or position-limiting device which provides a fail-safemechanical means to prevent the inadvertent destruction of the vacuumwithin the ion source region and also prevents jamming the specimen andfilament elements into the gate valve on insertion of the probe.

While a present exemplary embodiment of this invention has beenillustrated and described, it will be recognized that this invention maybe otherwise variously embodied and prac ticed by those skilled in theart.

' What we claim is:

l. A sample insertion vacuum lock and probe assembly for massspectrometers comprising in combination:

a contact-supporting plate having an aperture therethrough mountedwithin an ion chamber of a mass spectrometer, said plate being mountedin said ion chamber so that the aperture is in axial alignment with theion source and ion beam;

a plurality of electrical contact members mounted to said plate normalto the axis of the aperture area, each contact member having one endextending into the aperture area,

each of said contact members comprising an outer casing having anaxially stepped bore therethrough;

a slidable inner contact element mounted within each of the outercasings for slidable movement relative to the casing, one end of each ofsaid inner contact elements extending beyond the end of the casing andinto the aperture area;

resilient means mounted in each stepped bore for biasing each innercontact element into the aperture area;

means connecting each of said contact members to a source of electricalenergy, said means limiting the relative movement ofeach ofsaid innercontact elements;

vacuum lock assembly mounted exteriorly of the ion chamber, said vacuumlock being in axial alignment with the ion source and ion beam of theion chamber, said vacuum lock comprising a high-vacuum gate valvemounted exteriorly of the ion chamber;

a casing attached to said gate valve and extending axially outward fromsaid valve, said gate valve and said casing defining a concurrentaxially aligned passageway therethrough, said passageway being in axialalignment with an ion beam of the ion chamber;

a specimen-inserting probe sealingly mountable for reciprocal movementin said passageway for insertion and removal of specimens to be analyzedinto the ion chamber, said probe comprising a driving shaft portionsealingly insertable through the vacuum lock;

a forwardly projecting specimen carrier portion mounted at one end ofsaid driving shaft, said driving portion and carrier portion beingaxially aligned for direct axial alignment with the ion source and ionbeam upon insertion of the probe through the vacuum lock and into theion chamber, said carrier portion and said driving portion remainingattached during ion analysis;

a plurality of stationary contact elements secured to said carryingportion for slidable engagement with said slidable inner contactelements, each of said stationary contact elements being positionedabout the outer surface of the carrying portion for cooperativeengagement with a corresponding biased inner contact element whereinelectrical contact is made when the carrying portion is inserted throughsaid plate aperture area and electrical contact is broken when saidcarrying portion is removed from said plate aperture area;

a positioning member mounted adjacent the other end of said drivingshaft member;

evacuation means for providing staged evacuation of said vacuum lockassembly upon partial insertion of said probe through said passagewaywherein said vacuum lock assembly is evacuated to instrument vacuumpressure;

positioning means attached to the vacuum lock assembly for cooperativeengagement with said driving shaft providing fail-safe stops to limitingaxial movement of the insertion probe to prevent destruction of the ionchamber vacuum and providing proper alignment of said specimen carrier,

said positioning means comprising a clamp mounted on said casing;

a shaft pivotally mounted on said clamp;

means for adjusting said shaft position relative to said casguide meanssecured to said shaft for engagement with said position member toposition said specimen carrier portion thereby; and

wherein said filament means are aligned relative to the ion beam uponfull insertion of the specimen insertion probe into the ion chamber;

conducting means connecting said stationary contact elements with saidfilament means; and wherein said specimen carrier portion is formed of alow water adsorption ceramic.

(s/se) Patent: No.

Inventor(s) Dated June 29, 1971 Richard E. Perrin & Billy A. Hopper Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 1,

Column 3,

Column 4,

Column 4,

Column Column Cokumn Column Column 6,

line

line

line

line

line

line

line

line

line

"withdraw" should be withdrawn "1 x 10 should be 1 x 10' "vaLve" shouldbe valve "1 x 10 should be 1 x 10' "1 x 10 should be 1 X 10' "to" shouldbe for Signed and sealed this 28th day of December 1971.

(SEAL) Attest:

EDWARD M.FLETCHER,JR.

Attesting Officer ROBERT GOTTSCHALK Acting Commissioner of Patents

2. The combination as set forth in claim 1 further comprising filamentmeans secured to the end of said carrying portion wherein said filamentmeans are aligned relative to the ion beam upon full insertion of thespecimen insertion probe into the ion chamber; conducting meansconnecting said stationary contact elements with said filament means;and wherein said specimen carrier portion is formed of a low wateradsorption ceramic.